iOS - 在 Swift 3 中以编程方式删除和激活新约束时布局损坏

在 Swift 3 中以编程方式处理约束让我非常沮丧。在非常基本的层面上，我的应用程序显示了许多具有初始约束的 View ，然后在旋转时应用新约束，以允许 View 调整大小并根据需要重新定位。不幸的是，这远非易事，因为我还是 iOS 开发和 Swift 的新手。我花了很多时间尝试 StackOverflow 和其他地方提供的许多不同的解决方案，但我一直得到相同的结果(最后详述)。

我有一个 View Controller (我们称之为“主视图 Controller ”)，它的 Root View 包含两个 subview ， View A 和 View B 容器。 Root View 的背景颜色为粉红色。

View A 内部包含一个标签，垂直和水平居中，以及橙色背景色。 View A 有 4 个约束 - [Leading Space to Superview]、[Top Space to Top Layout Guide]、[Trailing Space to Superview] 和 [Bottom Space to Bottom Layout Guide]。

View B Container 最初没有内容。它有 4 个约束 - [Width Equals 240]、[Height Equals 128]、[Leading Space to Superview] 和 [Leading Space to Superview]。

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我还有另一个 View Controller (我们称之为“ View B View Controller ”)驱动 View B 容器的内容。为了简单起见，这只是一个没有自定义逻辑的默认 View Controller 。 View B View Controller 的 Root View 包含一个 subview View B。

View B 与上面的 View A 几乎相同 - 单个标签垂直和水平居中，背景颜色为蓝色。 View B 有 4 个约束 - [Leading Space to Superview]、[Top Space to Superview]、[Trailing Space to Superview] 和 [Bottom Space to Superview]。

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在主视图 Controller 类中，我维护了对 View A 和 View B Container 的 IBOutlet 引用，以及上面提到的它们各自的约束。在下面的代码中，主视图 Controller 实例化 View B View Controller 并将后续 View 添加到 View B 容器，应用灵活的宽度/高度自动调整大小掩码以确保其填充可用空间。然后它会触发对内部 _layoutContainers() 函数的调用，该函数根据设备的方向执行许多约束修改操作。当前的实现如下:

• 从 View A 中移除已知约束
• 从 View B Container 中移除已知约束
• 根据设备方向，根据特定设计激活 View A 和 View B Container 的新约束(在下面的代码注释中有详细说明)
• 针对所有 View 触发 updateConstraintsIfNeeded() 和 layoutIfNeeded()

当发生resize事件时，代码允许viewWillTransition()触发，然后在完成回调中调用_layoutContainers()函数，使设备处于一个新的状态并可以遵循必要的逻辑路径。

整个主视图 Controller 单元如下:

import UIKit

class ViewController: UIViewController {

    // MARK: Variables

    @IBOutlet weak var _viewAView: UIView!

    @IBOutlet weak var _viewALeadingConstraint: NSLayoutConstraint!
    @IBOutlet weak var _viewATopConstraint: NSLayoutConstraint!
    @IBOutlet weak var _viewATrailingConstraint: NSLayoutConstraint!
    @IBOutlet weak var _viewABottomConstraint: NSLayoutConstraint!

    @IBOutlet weak var _viewBContainerView: UIView!

    @IBOutlet weak var _viewBContainerWidthConstraint: NSLayoutConstraint!
    @IBOutlet weak var _viewBContainerHeightConstraint: NSLayoutConstraint!
    @IBOutlet weak var _viewBContainerTopConstraint: NSLayoutConstraint!
    @IBOutlet weak var _viewBContainerLeadingConstraint: NSLayoutConstraint!

    // MARK: UIViewController Overrides

    override func viewDidLoad() {
        super.viewDidLoad()

        // Instantiate View B's controller
        let viewBViewController = self.storyboard!.instantiateViewController(withIdentifier: "ViewBViewController")
        self.addChildViewController(viewBViewController)

        // Instantiate and add View B's new subview 
        let view = viewBViewController.view
        self._viewBContainerView.addSubview(view!)
        view!.frame = self._viewBContainerView.bounds
        view!.autoresizingMask = [.flexibleWidth, .flexibleHeight]

        viewBViewController.didMove(toParentViewController: self)

        self._layoutContainers()
    }

    override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
        super.viewWillTransition(to: size, with: coordinator)

        coordinator.animate(alongsideTransition: nil, completion: { _ in
            self._layoutContainers()
        })
    }

    // MARK: Internal

    private func _layoutContainers() {

        // Remove View A constraints
        self._viewAView.removeConstraints([
            self._viewALeadingConstraint,
            self._viewATopConstraint,
            self._viewATrailingConstraint,
            self._viewABottomConstraint,
        ])

        // Remove View B Container constraints
        var viewBContainerConstraints: [NSLayoutConstraint] = [
            self._viewBContainerTopConstraint,
            self._viewBContainerLeadingConstraint,
        ]

        if(self._viewBContainerWidthConstraint != nil) {
            viewBContainerConstraints.append(self._viewBContainerWidthConstraint)
        }
        if(self._viewBContainerHeightConstraint != nil) {
            viewBContainerConstraints.append(self._viewBContainerHeightConstraint)
        }

        self._viewBContainerView.removeConstraints(viewBContainerConstraints)


        // Portrait:
        // View B - 16/9 and to bottom of screen
        // View A - anchored to top and filling the remainder of the vertical space

        if(UIDevice.current.orientation != .landscapeLeft && UIDevice.current.orientation != .landscapeRight) {

            let viewBWidth = self.view.frame.width
            let viewBHeight = viewBWidth / (16/9)
            let viewAHeight = self.view.frame.height - viewBHeight

            // View A - anchored to top and filling the remainder of the vertical space
            NSLayoutConstraint.activate([
                self._viewAView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
                self._viewAView.topAnchor.constraint(equalTo: self.view.topAnchor),
                self._viewAView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor),
                self._viewAView.bottomAnchor.constraint(equalTo: self._viewBContainerView.topAnchor),
            ])

            // View B - 16/9 and to bottom of screen
            NSLayoutConstraint.activate([
                self._viewBContainerView.widthAnchor.constraint(equalToConstant: viewBWidth),
                self._viewBContainerView.heightAnchor.constraint(equalToConstant: viewBHeight),
                self._viewBContainerView.topAnchor.constraint(equalTo: self.view.topAnchor, constant: viewAHeight),
                self._viewBContainerView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
            ])
        }

        // Landscape:
        // View B - 2/3 of screen on left
        // View A - 1/3 of screen on right
        else {
            let viewBWidth = self.view.frame.width * (2/3)

            // View B - 2/3 of screen on left
            NSLayoutConstraint.activate([
                self._viewBContainerView.widthAnchor.constraint(equalToConstant: viewBWidth),
                self._viewBContainerView.heightAnchor.constraint(equalToConstant: self.view.frame.height),
                self._viewBContainerView.topAnchor.constraint(equalTo: self.view.topAnchor),
                self._viewBContainerView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
            ])

            // View A - 1/3 of screen on right
            NSLayoutConstraint.activate([
                self._viewAView.leadingAnchor.constraint(equalTo: self._viewBContainerView.trailingAnchor),
                self._viewAView.topAnchor.constraint(equalTo: self.view.topAnchor),
                self._viewAView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor),
                self._viewAView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor)
            ])
        }

        // Fire off constraints and layout update functions

        self.view.updateConstraintsIfNeeded()
        self._viewAView.updateConstraintsIfNeeded()
        self._viewBContainerView.updateConstraintsIfNeeded()

        self.view.layoutIfNeeded()
        self._viewAView.layoutIfNeeded()
        self._viewBContainerView.layoutIfNeeded()
    }
}

---

我的问题是，虽然应用程序的初始加载显示了预期的结果( View B 保持 16/9 比例并位于屏幕底部，但 View A 占用了剩余空间):

任何后续的旋转都会完全破坏 View 并且不会恢复:

此外，一旦加载应用程序，就会引发以下约束警告:

TestResize[1794:51030] [LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<_UILayoutSupportConstraint:0x600000096c60 _UILayoutGuide:0x7f8d4f414110.height == 0   (active)>",
    "<_UILayoutSupportConstraint:0x600000090ae0 V:|-(0)-[_UILayoutGuide:0x7f8d4f414110]   (active, names: '|':UIView:0x7f8d4f40f9e0 )>",
    "<NSLayoutConstraint:0x600000096990 V:[_UILayoutGuide:0x7f8d4f414110]-(0)-[UIView:0x7f8d4f413e60]   (active)>",
    "<NSLayoutConstraint:0x608000094e10 V:|-(456.062)-[UIView:0x7f8d4f413e60]   (active, names: '|':UIView:0x7f8d4f40f9e0 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600000096990 V:[_UILayoutGuide:0x7f8d4f414110]-(0)-[UIView:0x7f8d4f413e60]   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.



TestResize[1794:51030] [LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<NSLayoutConstraint:0x600000096940 UIView:0x7f8d4f413e60.leading == UIView:0x7f8d4f40f9e0.leadingMargin   (active)>",
    "<NSLayoutConstraint:0x608000094e60 H:|-(0)-[UIView:0x7f8d4f413e60]   (active, names: '|':UIView:0x7f8d4f40f9e0 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600000096940 UIView:0x7f8d4f413e60.leading == UIView:0x7f8d4f40f9e0.leadingMargin   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.



TestResize[1794:51030] [LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<_UILayoutSupportConstraint:0x600000096d50 _UILayoutGuide:0x7f8d4f40f4b0.height == 0   (active)>",
    "<_UILayoutSupportConstraint:0x600000096d00 _UILayoutGuide:0x7f8d4f40f4b0.bottom == UIView:0x7f8d4f40f9e0.bottom   (active)>",
    "<NSLayoutConstraint:0x600000092e30 V:[UIView:0x7f8d4f40fd90]-(0)-[_UILayoutGuide:0x7f8d4f40f4b0]   (active)>",
    "<NSLayoutConstraint:0x608000092070 UIView:0x7f8d4f40fd90.bottom == UIView:0x7f8d4f413e60.top   (active)>",
    "<NSLayoutConstraint:0x608000094e10 V:|-(456.062)-[UIView:0x7f8d4f413e60]   (active, names: '|':UIView:0x7f8d4f40f9e0 )>",
    "<NSLayoutConstraint:0x600000096e40 'UIView-Encapsulated-Layout-Height' UIView:0x7f8d4f40f9e0.height == 667   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600000092e30 V:[UIView:0x7f8d4f40fd90]-(0)-[_UILayoutGuide:0x7f8d4f40f4b0]   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.



TestResize[1794:51030] [LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<_UILayoutSupportConstraint:0x600000096c60 _UILayoutGuide:0x7f8d4f414110.height == 20   (active)>",
    "<_UILayoutSupportConstraint:0x600000090ae0 V:|-(0)-[_UILayoutGuide:0x7f8d4f414110]   (active, names: '|':UIView:0x7f8d4f40f9e0 )>",
    "<NSLayoutConstraint:0x600000096850 V:[_UILayoutGuide:0x7f8d4f414110]-(0)-[UIView:0x7f8d4f40fd90]   (active)>",
    "<NSLayoutConstraint:0x608000093b50 V:|-(0)-[UIView:0x7f8d4f40fd90]   (active, names: '|':UIView:0x7f8d4f40f9e0 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600000096850 V:[_UILayoutGuide:0x7f8d4f414110]-(0)-[UIView:0x7f8d4f40fd90]   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

感谢您阅读到这里!肯定有人遇到过(并希望解决)这个或类似的问题。任何帮助将不胜感激!

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Best Answer-推荐答案

与其尝试添加和删除约束，不如考虑调整优先级来转换您的 View 。

所以对于您来说，默认布局有一个优先级为 900 的约束。然后添加第二个优先级为 1 的冲突约束。现在要切换显示模式，只需将第二个约束优先级移动到 900 以上，然后返回到下方以反转。只需更改优先级，即可在 Interface Builder 中轻松测试所有内容。

您还可以将更改放在动画 block 中以获得良好的平滑过渡。

-

要考虑使用的另一件事是尺寸等级。使用它，您可以指定特定约束仅适用于某些方向，这样您就可以完全“免费”获得所需的行为，只需在 IB 中进行设置。

关于iOS - 在 Swift 3 中以编程方式删除和激活新约束时布局损坏，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/45096359/